Combined treatment with chlorine dioxide gas,fumaric acid,and ultraviolet-C light for inactivating Escherichia coli O157:H7 and Listeria monocytogenes inoculated on plums

Combined non-thermal treatment with chlorine dioxide (ClO₂) gas, ultraviolet-C (UV-C) light, and fumaric acid was performed to inactivate Listeria monocytogenes and Escherichia coli O157:H7 inoculated on plums. Plums were treated with ClO₂ gas (15 and 30 ppmv), fumaric acid (0.1, 0.3, and 0.5%), and by UV-C irradiation (3, 5, and 10 kJ/m²). The single treatments with 15 or 30 ppmv ClO₂ gas, 0.5% fumaric acid, and 10 kJ/m² UV-C decreased the population of L. monocytogenes by 1.78, 2.00, 1.65, and 1.62 log CFU/g, respectively, and the population of E. coli O157:H7 by 1.73, 1.81, 1.34, and 2.07 log CFU/g, respectively. In addition, combined treatments reduced the populations of the pathogenic bacteria more than each treatment alone. In particular, the combined treatment with ClO₂ gas (30 ppmv) for 20 min, fumaric acid (0.5%), and UV-C (10 kJ/m²) decreased the populations of L. monocytogenes and E. coli O157:H7 by 6.26 and 5.48 log CFU/g, respectively. These results suggest that combined treatment with ClO₂ gas, UV-C light, and fumaric acid may be a useful hurdle technology to enhance the microbiological safety of plums.     

In vitro binding of bile acids by blueberries (Vaccinium spp.), plums (Prunus spp.), prunes (Prunus spp.), strawberries (Fragaria X ananassa), cherries (Malpighia punicifolia), cranberries (Vaccinium macrocarpon) and apples (Malus sylvestris)

The in vitro binding of bile acids by blueberries (Vaccinium spp.), plums (Prunus spp.), prunes (Prunus spp.), strawberries (Fragaria X ananassa), cherries (Malpighia punicifolia) cranberries (Vaccinium macrocarpon) and apples (Malus sylvestris) was determined using a mixture of bile acids secreted in human bile at a duodenal physiological pH of 6.3. Six treatments and two blank incubations were conducted to testing various fresh raw fruits on an equal dry matter basis. Considering cholestyramine (bile acid binding, cholesterol lowering drug) as 100% bound, the relative in vitro bile acid binding on dry matter (DM), total dietary fiber (TDF) and total polysaccharides (PCH) basis was for blueberries 7%, 47% and 25%; plums 6%, 53% and 50%; prunes 5%, 50% and 14%; strawberries 5%, 23% and 15%; cherries 5%, 37% and 5%; cranberries 4%, 12% and 7%; and apple 1%, 7% and 5%, respectively. Bile acid binding on DM basis for blueberries was significantly (P ? 0.05) higher than all the fruits tested. The bile acid binding for plums was similar to that for prunes and strawberries and significantly higher than cherries, cranberries and apples. Binding values for cherries and cranberries were significantly higher than those for apples. These results point to the relative health promoting potential of blueberries > plums = prunes = strawberries = cherries = cranberries > apples as indicated by their bile acid binding on DM basis. The variability in bile acid binding between the fruits tested maybe related to their phytonutrients (antioxidants, polyphenols, hydroxycinnamic acids, flavonoids, anthocyanins, flavonols, proanthocyanidins, catechins), structure, hydrophobicity of undigested fractions, anionic or cationic nature of the metabolites produced during digestion or their interaction with active binding sites. Inclusion of blueberries, plums, prunes, strawberries, cherries and cranberries in our daily diet as health promoting fruits should be encouraged. Animal studies are planned to validate in vitro bile acid binding of fruits observed herein to their potential of atherosclerosis amelioration (lipid and lipoprotein lowering) and cancer prevention (excretion of toxic metabolites).     

Optimised processing technique for colour- and cloud-stable plum juices and stability of bioactive substances

Plum (Prunus domestica) juices were produced from different cultivars with optimised processing technology. High results for dry mass (19–21 °Brix), sugar-free extract (75–105 g/L), total acidity (6–11 g/L), sorbitol (27–52 g/L) and minerals were found. Secondary plant metabolites were present in high amounts as well. By means of HPLC/PDA 1465–2590 mg/L of colourless polyphenols were found. Neochlorogenic acid, chlorogenic acid, (+)-catechin and (−)-epicatechin were the predominant polyphenols. Total anthocyanins were found in amounts of 43–168 mg/L in the fresh juices. They were identified as cyanidin-3-glucoside, cyanidin-3-rutinoside, peonidin-3-glucoside and peonidin-3-rutinoside. A fast decline of the anthocyanin concentrations could be observed during a 6 months storage at 20 °C, which changed the red colour of the juices drastically. Beside high polyphenol concentrations, high antioxidant capacities of the juices were determined as well. The applied processing technology allowed the production of cloud-stable plum nectars.     

Extractable antioxidants and non-extractable phenolics in the total antioxidant activity of selected plum cultivars (Prunus domestica L.): Evolution during on-tree ripening

The purpose of this study was to evaluate the contribution of extractable antioxidants and non-extractable phenolics to the total antioxidant activity (TAA) of plums. Therefore, the antioxidant activity was determined (ABTS assay) in aqueous–organic extracts, as well as in the extraction residues which were a subject of two different acidic treatments to release hydrolysable tannins and non-extractable proanthocyanidins (NEPA). In addition, the changes in TAA during the last week of ripening were investigated. Extractable antioxidants contributed less than 18% to the TAA, considerably higher values of antioxidant activity were associated with hydrolysable tannins and NEPA, suggesting that the antioxidant activity of plums may be underestimated in the literature. The ripening resulted in an increase of TAA up to 38% in excess of the value determined on the first sampling date. TAA showed a similar pattern over the ripening period for all cultivars studied.